Such a control system comprises a linkage having elements that are arranged and connected together in such a manner as to transmit movements from a flight control, such as a control stick, to the control surfaces. By way of example, one of the transmission elements is a forced-transmission link for actuating a hydraulic power assistance servo-valve. The linkage also includes a spring enabling force to be returned that can be perceived by the pilot via the control stick and that is proportional to the force exerted by the pilot on the stick.
Proposals have been made to use an electric motor to act simultaneously to provide trim, and to replace the servo-valve and the spring. With the servo-valve being eliminated, the motor must then provide the necessary power assistance function. For these purposes, control of the electric motor requires measurements to be available of the forces exerted by the pilot on the control stick.
One way in which such measurements can be obtained is to install strain gauges on the transmission link in order to measure the forces exerted thereon. Nevertheless, such strain gauges need to be stuck directly onto the link in order to perform their function and that kind of fastening is not sufficiently reliable and durable for certain applications, in particular in aviation.
It is also known to provide elastically-deformable zones in the body of the link that allow two portions of the body of the link to move relative to each other, which portions are associated with a movement detector element. The structure of known devices does not make it possible in simple and effective manner to sense external stresses.